Which language is more difficult to study: Chinese, Finnish or the language of some small Indiana folk?
The comparing questions are always too difficult. You have to have people who really good knows all the products which you want to compare. Moreover you should define which part of the product you plan to use just now and which could be important in the future. Do you use JSON or XML data for the grid input or you use local JavaScript data? Do you need to use standard grid or grid with subgrids, treegrid or a grid with grouping?
Before you not define the area of the usage of the grid more clear you will not receive any good answer. At the end is sometime could be even important which know-how you have currently and just which documentation or examples you can easy understand and use yourself. The experience of other people which you can use could be more important as the features of the product. If you look at the number of questions on the stackoverflow.com with the tags "jqgrid" and with the tag "slickgrid" you can see in what product could help you stackoverflow
